I went through 3 drain and refills on my 69 ranger before I got the air out. Best money I've spent was a 1.00 heater hose fitting between the intake and the firewall. It has a screw on cap and on mine I attach a bungee cord to heater hose and the bottom of hood to pull it above the rest of the cooling system. Fire it up, crack the cap just a bit and once it warms up it burps itself.

Shroud would be pretty important as mentioned.

Also, my problems were complicated by an orginal radiator. Once I replaced that I can't get it above 190 even sitting in traffic in 98 degrees.

Correct coolant mix and good cap matter as well.

Good luck!